Power tools such as an air powered screw driver, nutsetter, or similar air operated tool frequently depend on shutoff devices responsive to sensing motor pressure, which is low when the tool is running free, and which rises as the tool is loaded. I.e., in a given tool, torque is a positive function of air pressure. Increasing pressure increases torque. In an air tool, torque is a negative function of speed, and this function is linear. When setting a fastener, e.g., as torque builds up, speed goes down; when speed is zero or at stall, torque is highest.
To control maximum motor operating pressure, a stall torque regulator has been known to be located in the tool at a motor inlet.